1. Field of the Invention
The present invention relates to an inertial drive actuator which stepping-drives a mobile object.
2. Description of the Related Art
There is known an inertial drive actuator which supplies a saw-toothed drive pulse to an electromechanical conversion element coupled to a drive shaft to displace the drive shaft in an axial direction and to move a mobile object frictionally coupled to the drive shaft in the axial direction.
This inertial drive actuator is disclosed in, for example, U.S. Pat. No. 5,225,941. As shown in FIG. 1 in the U.S. Patent, a driving rod serving as a vibrating member is inserted into a hole formed in an upright portion of a supporting member and movably arranged in an axial direction of the vibrating member. One end of the vibrating member is fixed to one end of a piezoelectric element. The other end of the piezoelectric element is fixed to the supporting member. Therefore, with vibration of the piezoelectric element, the vibrating member vibrates in the axial direction. A lens barrel serving as a mobile object has two holes formed therein, and the vibrating member is inserted into the holes. Furthermore, a leaf spring is fitted on the mobile object from beneath, and a curved projection which is a projecting portion formed on the leaf spring is brought into press contact with the vibrating member. In this manner, the mobile object and the vibrating member are frictionally coupled to each other by being pressed by the leaf spring.
In the inertial drive actuator, as shown in FIG. 3(A) in the U.S. Patent, a drive voltage waveform has a sharply upright portion and a moderately fall portion. In the sharply upright portion, the piezoelectric element sharply extends to rapidly move the mobile object fixed to the piezoelectric element. However, the mobile object overcomes frictional coupling force between the mobile object and the vibrating member by the inertia to stay at the position without moving. When the piezoelectric element moderately shrinks, the vibrating member fixed to the piezoelectric element slowly moves. In this case, with frictional force between the mobile member brought into press contact with the leaf spring and the vibrating member, the mobile object moves along with movement of the vibrating member.
As described above, the inertial drive actuator is an actuator which can move the mobile object by the frictional coupling between the mobile object and the vibrating member generated by the leaf spring and application of a voltage having the drive voltage waveform.
When the leaf spring always brings the vibrating member into press contact with the mobile object to frictionally support the mobile member to keep the position thereof when the mobile object is stopped.